The present invention relates generally to fast-acting herbicidal compositions or formulations containing glyphosate, and to methods of using such compositions to kill or control the growth and proliferation of unwanted plants.
Herbicidal compositions containing the herbicide N-(phosphonomethyl)glycine (commonly referred to as glyphosate) or its derivatives are useful for killing or suppressing the growth of unwanted plants such as grasses, weeds and the like. The herbicidal properties of glyphosate and its derivatives were discovered by Franz and patented in U.S. Pat. Nos. 3,799,758 and 4,405,531. Glyphosate herbicidal formulations are typically applied to the foliar tissues (i.e., the leaves or other photosynthesizing organs) of the target plant by spray application. After application, the glyphosate is absorbed by the foliar tissues and translocated throughout the plant. Glyphosate noncompetitively blocks an important biochemical pathway which is common to virtually all plants, but which is absent in animals. Although glyphosate is very effective in killing or controlling the growth of unwanted plants, the uptake (i.e., absorption) of glyphosate by the plant foliar tissue and translocation of glyphosate throughout the plant is relatively slow. Visually apparent phytotoxic effects or burndown symptoms (e.g., yellowing, browning, wilting etc.) may not appear until one week or more after a plant has been treated with glyphosate or its derivatives.
Given the relatively limited water solubility of the organic acid N-(phosphonomethyl)glycine, aqueous herbicidal compositions are typically formulated using one or more of the more water-soluble and acceptable salts or other derivatives of glyphosate. Furthermore, these compositions typically further contain one or more surfactants to enhance their effectiveness for foliar application. When water is added to a composition formulated with surfactants, the resulting sprayable composition more easily and effectively covers the foliar tissues of plants. Therefore, glyphosate salts, have been formulated with various surfactants such as polyoxyalkylene-type surfactants (e.g., with a polyoxyalkylene alkylamine, and in particular a polyoxyethylene tallowamine). Monsanto Company markets commercial formulations of glyphosate with such surfactants under the trademark ROUNDUP.
Nevertheless, because of the somewhat slow development of visual symptoms of plant suppression or death that result when glyphosate is utilized alone or even with a surfactant, various alternative herbicidal formulations have been suggested to induce earlier visual symptoms of treatment. Early symptom-producing or fast-acting, ready-to-use (RTU) compositions are particularly desired in the lawn and garden market where the consumer appreciates relatively immediate evidence that the product is having the desired effect.
Attempts at inducing earlier visual symptomology have included combining glyphosate or its derivatives with certain fatty acids or their herbicidally active salts, for example, pelargonic acid (PA; also referred to as nonanoic acid), capric acid (also referred to as decanoic acid) and mixtures of such fatty acids or salts thereof as described, for example, in U.S. Pat. Nos. 5,196,044 (Caulder, et al.) and 5,994,269 (Bugg, et al.), International Publication No. WO 92/07467, European Patent Application Publication No. 0 577 914, and by Kristin A. Arnold, et al. in “Improved Early Symptom Development with a Ready-To-Use Glyphosate Formulation by Addition of Fatty Acid,” Pesticide Science, 38(2-3), pp. 270-272 (1993). It is suggested that such a combination provides a herbicidal formulation capable of inducing fast symptomology in the treated plants due to the fatty acid component and prolonged control due to the glyphosate component. Indeed some success has been achieved along these lines in RTU formulations available from Monsanto Company and other manufacturers.
However, despite some degree of success in providing herbicidal compositions that accelerate the appearance of visual phytotoxic effects, there remains a need, particularly in the RTU market segment, for improved glyphosate formulations providing even faster symptomology. Moreover, previous attempts, while inducing earlier visual effects on treated plants, have sometimes suffered from less than expected or desired long-term control, perhaps due to unintended antagonism to the glyphosate component by other ingredients of the herbicidal composition. Still further, difficulty has been encountered in providing fast-acting glyphosate compositions that resist separation of the active ingredients and other components of the formulation from the aqueous solution upon prolonged storage and that can be readily formulated as a concentrate.